1. Field of the Invention
This invention relates to magnetic field measurement, and in particular to detection of a magnetic field due the presence of a magnetic object or due to the presence of an anomaly discontinuity in a moving conductive sheet.
2. Description Relative to the Prior Art
A wide variety of devices for detection of a magnetic object exist in the art. Applications widely range from detecting the position of teeth in a rotating gear, (U.S. Pat. No. 5,304,926) to measuring the separation of a railroad car axle from the railroad track (U.S. Pat. No. 4,943,772). The technique employed and the configuration of the implemented hand are strongly depend upon the size of the object to be detected, and its separation from the measurement device.
The present invention is directed towards the detection of a small magnetic object under conditions where the detector may be brought into close proximity to the region thought to include the magnetic particle. It may be applied in the medical field there doctors need a means to sense the presence of foreign magnetic material within a patient, particularly within the eyes, before placing the patient in the large magnetic field of a diagnostic scanner. The large field gradient of the scanner can cause the magnetic object to move and inflict injury. The invention can also be used before and during surgery to detect and locate a magnetic object within a patient.
The structure of the present invention may also be used to detect an anomaly in the eddy current magnetic field due to a crack or other discontinuity in a moving planar sheet of electrically conductive material.